Air purification respirators (“APRs”), commonly referred to as “gas masks,” are in wide private and military use. APRs are wearable filtering devices used to create an envelope of clean air around at least a wearer's nose and mouth, providing protection to the wearer from the inhalation of undesired or harmful dust, fumes, vapors, or other gases.
APRs have multiple applications, particularly in the industrial and military fields. APRs are used in industry to protect workers from airborne industrial hazards such as fumes, gasses, dust, and particulate matter. Representative industrial uses would include in paint booths, grain storage facilities, and laboratories. In the military, APRs are employed to protect personnel who may be exposed to attack by poison gas or other airborne toxins.
APRs are generally manufactured in the form of a mask that covers at least the wearer's mouth and nose. APRs can include additional protective surfaces to guard the wearer's eyes, ears, facial skin, or even hair. When properly fitted and worn by a wearer, an APR creates an envelope of clean air within the APR by, in part, forming a seal between the APR and the wearer's face that substantially prohibits the entry of air from the outside environment. As a result, the air breathed by the wearer during use of the APR is, except for minimal leakage through the facial seal, the intake ports, or the exhalation valve, air that has been cleaned by filters connected to the APR intake ports or air that has been provided directly from a known clean air source such as an air tank.
APRs generally have one or more intake ports, usually disposed towards the sides of the mask apparatus. A filter apparatus or canister can be fitted into the intake port, usually by a sealing threaded connection or a sealing press-fit connection. Both filter ports can be fitted with filter apparatuses, or one can be so fitted and the other sealed shut with a threaded cap. This general modularity allows filters to be changed quickly and conveniently, and allows different filtering apparatus to be installed to optimize an APR for different environments. The ability to quickly replace filters also reduces cost by allowing the same APR mask body to be re-used even if the filters have to be replaced or changed. Alternatively, one or both intake ports can be coupled to a hose leading to a known clean air source, such as an air take.
APRs generally include a means to allow the wearer's exhaled breath to escape, most typically an outlet port disposed on a central portion of the mask. The outlet port of the APR typically comprises a port, generally round in shape, disposed over the area of the wearer's mouth. In many APRs in common use, this port includes one-way valve assembly, such as a flap valve, configured to allow air to escape from the APR during the wearer's exhalation, but which prevents air from the outside environment from entering the APR during inhalation. This one-way valve assembly is often removable via a sealing snap-on or sealing interference fit with the lip of the outlet port of the APR. In one common configuration, the outlet port of the APR includes a spoke-and-hub structures in which spokes support a donut-shaped hub in the center of the port opening. The hole in the center of the hub is sized to accept the stem of a mushroom-style membrane, which stem presses into the hole in the center of the hub and is there retained, with the membrane in general contact with the spokes of the spoke-and-hub structure and in generally sealed contact with a circumferential rim around the edge of the outlet port. The membrane is shaped and sized to cover the outlet port opening and a portion of this circumferential rim. When a wearer exhales, exhalation pushes the membrane away from the spoke-and-hub structure and from the rim, allowing the exhaled air to escape through the exhalation port. At other times, and particularly when a wearer inhales, the membrane is pulled by negative pressure against the spoke-and-hub structure and the circumferential rim, sealing the outlet port so that air from the outside environment (other than leakage in acceptable volumes, as would be known by one skilled in the art) does not enter the clean air envelope defined by the mask.
APRs may be either positive pressure or negative pressure devices. A positive pressure APR typically includes an external pump or pressurized vessel that forces clean air into the APR through an intake port. Positive pressure creates a more positively sealed clean air envelope, since the pressure within the clean air envelope is higher than the pressure of the external air. Such positive pressure reduces the occurrence of seepage or leakage of air from the outside environment into the clean air envelope of the APR.
A negative pressure APR is more common and less expensive, and uses the negative pressure generated by the wearer's inhalation to assist with sealing the APR to the wearer's face. A wearer's inhalation generates negative pressure inside the clean air envelope as it draws air into the APR through the intake ports. Filter apparatus attached to the intake ports clean air from the outside environment before it passes into the clean air envelope. The negative pressure generated by inhalation assists with maintaining the seal between the APR and the wearer's face and assists with maintaining the seal formed by the outlet port valve.
One disadvantage common to APRs is impairment of the wearer's ability to speak clearly or audibly. Maintenance of a clean air envelope within the APR restricts the volume of air going into or out of the APR. Even exhaled air must pass through a one-way valve before it reaches the outside environment. As a result, the volume of sound generated by a wearer's speech or other vocalizations is notably diminished to listeners, and such vocalizations may be garbled and difficult to understand. This impairment to clear and audible speech is a detriment in many of the APRs typical applications, particularly in military and industrial contexts where clear and audible communication may be imperative.
Several attempts to mitigate this impairment to a wearer's ability to speak and be heard clearly while wearing an APR are known to the art. Some APRs are equipped with a diaphragm element in proximity to the outlet port that acts as a mechanical emitter to more efficiently transmit vibrations created by the wearer's speech from the clean air envelope within the APR to the outside environment without allowing untreated air to pass into the APR. While diaphragms facilitate some improvement in sound transmission, they still result in speech that is largely muted, muffled, and difficult to understand.
Alternate attempts to solve this problem are disclosed by, for example, U.S. Pat. No. 5,463,693. These solutions involve amplifiers, microphones, or both, adapted to fit either on the outlet or inlet port of an APR (externally mounted solutions) or within the clean air envelope (internally mounted solutions). These known solutions generally require substantial modification of the APR, which is a disadvantage if clear vocalization is desired as an optional, but not a mandatory feature, for the APR. The modification to the APR required by these solutions also risks compromise of the integrity of the clean air envelope seal and does not allow a standard APR to be adapted quickly to allow improved vocal transmission. Further, since externally mounted solutions attempt generally to amplify sound transmitted through the APR, they still result in muted and muffled speech. Internally mounted solutions also often require piercing of components of the APR for the passage of wires or other structures, threatening the integrity of the clean air envelope.
It would be a decided advantage to have an enhanced speech transmission device that can be readily attached to an existing APR produced in large quantities, which places a microphone inside of the wearer's clean air envelope, but does not require piercing any portion of the APR, does not require substantial modification of the APR, and enables the wearer to transmit clear speech without substantial muting or muffling.